The growing demand for high-strength polymer materials has enhanced the importance of reinforced filled polymers. Such reinforcers as glass and mineral fiber, metals, oxides or metals, etc. help to improve the properties of polymers. To produce a high-strength polymer, it is necessary to ensure good adhesion of the filler to the polymer. There are different compounds, referred to as finishing agents, that help to improve the adhesion. There are bifunctional monomer compounds which react with both the mineral filler and the polymer. A finishing agent is normally applied onto the surface of a filler; a filler may be treated with vapor of a finishing agent; finally, a filler may be mixed with a powdered finishing agent. After such a treatment, the filler is added to the polymer. According to another technique, a finishing agent is introduced into the polymer where it is driven to the surface of the filler in the course of mixing. Filled polymers thus produced exhibit improved mechanical properties and increased aging resistance under severe conditions (cf. G. D. Andreyevskaya, "Vysokoprochnye orientirovannye stekloplastiki" /"Oriented High-Strength Glass-Rein-forced Plastics"/, Nauka Publishers, Moscow, 1966, p. 240; "Armirovannye polymernye materialy" /"Reinforced Polymer Materials"/, Collected Reviews and Translations from Foreign Periodicals, Mir Publishers, 1968, pp. 91, 122; "Synteticheskiye polymernye materialy" /"Synthetic Polymer Materials"/, Express Information Bulletin, Nos 36 and 38, 1976).
There is known a method for producing mineral fillers for polymers, such as polystyrene, polyethylene, and polypropylene, whereby mineral fillers are treated at a temperatue of 50.degree. to 150.degree. C. with finishing agents which are organosilicon compounds of the formula: EQU R.sub.4-y SiX.sub.y,
where R is an organic functional group capable of reacting with the polymer; X is a halogen, or an alkoxy or an acyloxy group; and y=1, 2, 3 (cf. Reviews in Polymer Technology, ed. by J. Skeist, 1, New York, 1972, pp. 1-49).
However, in order to ensure satisfactory physico-mechanical properties of filled polymers, one must select finishing agents containing specific R and X groups which are determined by the type of filler and the type of polymer. Besides, finishing agents of the above structure cannot be used for different types of polymers.
There is further known a method for producing mineral fillers containing graft peroxide groups and intended for polyethylene and polysulfones. According to this method, mineral fillers are treated with a finishing agent of the general formula: EQU CH.sub.2 =CHSi[OOC(CH.sub.3).sub.3 ].sub.3,
which is an organosilicon peroxide. The finishing agent is applied onto the mineral filler which is then added to a polymer at a temperature of 175.degree. to 230.degree. C. The heated peroxide produces free radicals which initiate the grafting of the polymer to the filler (cf. Mod. Plast. Intern., 6, No 6, pp. 28, 31 /1976/).
The application of the foregoing finishing agent is limited because of the high decomposition temperature of the organosilicon peroxide. This finishing agent is readily hydrolyzable by air moisture and calls for special storage conditions. Besides, the synthesis of this finishing agent is a complicated and costly process.
The literature offers no information on methods for producing mineral polymer fillers containing graft peroxide groups.